ExperimentalGeneral Remarks. All manipulations were performed in air, except where otherwise noted. The solvents thf and hexane (analytical grade) were freshly distilled from sodium/potassium alloy, dichloromethane was distilled from calcium hydride, the other solvents (acetonitrile, diethylether, acetone) were used as purchased. Deuterated solvents for NMR measurements were distilled from the appropriate drying agents under N 2 immediately prior to use following standard literature methods. 15 Air-sensitive compounds were stored and weighed in a glovebox. The reagents 1,2-dibromoethane, 1,3dibromopropane, 1,4-diiodobutane, 2,6-dimethylaniline, 2,4,6-trimethylaniline, 2,6-diisopropylaniline, triethylorthoformate, sodium tetrafluoroborate, and potassium bis(trimethylsilyl)amide were used as received. 1 H and 13 C NMR spectra were obtained on Bruker Avance AMX 400, 500 or Jeol Eclipse 300 spectrometers. The chemical shifts are given as dimensionless values and are frequency referenced relative to TMS. Coupling constants J are given in hertz (Hz) as positive values regardless of their real individual signs. Abbreviations used: st = septet, br = broad. Mass spectra (MS) and high-resolution mass spectra (HRMS) were obtained in positive electrospray (ES) mode unless otherwise reported, on a Waters Q-TOF micromass spectrometer. 1,3-Bis-(2,4,6-trimethylphenyl)-4,5,6,7-tetrahydro-3H-[1,3]diazepin-1-ium iodide, 7-Mes•HI. The reaction was performed on a 71.0 mmol scale of amidine (19.90 g), 5.00 g of K 2 CO 3 (36.0 mmol) and 22.00 g of 1,4-diiodobutane (71.0 mmol) in 1 L of acetonitrile. The solution was heated under reflux for 5 hours to yield 29.20 g (63.0 mmol, 89%) of white, crystalline material. 1,3-Bis-(2,6-dimethylphenyl)-4,5,6,7-tetrahydro-3H-[1,3]diazepin-1-ium iodide, 7-Xyl•HI. The reaction was performed on a 43.3 mmol scale of amidine (10.93 g), 5.8 mL of 1,4-diiodobutane (13.63 g, 44 mmol), 3.01 g of K 2 CO 3 (22.5 mmol) in 0.5 L of acetonitrile. The solution was heated under reflux for 5 hours to yield 14.85 g (34.2 mmol, 79%) of white, crystalline material. 1,3-Bis-(2,6-diisopropylphenyl)-4,5,6,7-tetrahydro-3H-[1,3]diazepin-1-ium iodide, 7-Pr i •HI. The reaction was performed on a 11.0 mmol scale of amidine (4.00 g), 0.78 g of K 2 CO 3 (5.6 mmol), 1.6 mL of 1,4-diiodobutane (3.76 g, 12.1 mmol) in 400 mL of acetonitrile. The solution was heated under reflux for 17 hours to yield 3.87 g (7.1 mmol, 64%) of white, crystalline material. 2,4-Bis-(2,4,6-trimethylphenyl)-4,5-dihydro-1H-benzo[e][1,3]diazepin-2-ium bromide, Xyl7-Mes•HBr. The reaction was performed on a 35.8 mmol scale of amidine (10.03 g), 36.0 mmol of , 'dibromo-o-xylene (9.49 g), 2.49 g of K 2 CO 3 (18.0 mmol) in 0.5 L of acetonitrile. The solution was heated under reflux for 5 hours to yield 12.42 g (26.2 mmol, 73%) of white, crystalline material. 1 H

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Wrong way round: Imidazolium salts blocked at C2 undergo oxidative addition to a Pt0 center at C4/C5 (see scheme; nbe=norbornene, IMes=1,3‐bis(2,4,6‐trimethylphenyl)imidazolin‐2‐ylidene). The resulting carbene ligands, which are bound the “wrong way” are susceptible, in common with their “normal” counterparts, to reductive elimination reactions to regenerate Pt0 complexes and imidazolium salts.

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Appropriate linking of Lewis acidic and Lewis basic components—in this case boronic acid and tertiary amine functionalities—allows the construction of a robust organometallic receptor capable of selectively binding hydrogen fluoride. This system can differentiate between exposure to HF and to related acids, such as HCl, by providing opposing electrochemical responses (see picture).

A systematic investigation of fluoride anion binding properties as a function of chelate backbone has been carried out for ferrocene functionalised boronic esters of the types FcB(OR)2 and fc[B(OR)2]2 [Fc = ferrocenyl = (eta5-C5H5)Fe(eta5-C5H4); fc = ferrocendiyl = Fe(eta5-C5H4)2]. Cyclic boronic esters containing a saturated five- or six-membered chelate ring are readily synthesized from ferrocene, and selectively bind fluoride via Lewis acid/base chemistry in chloroform solution. The resulting complexes are characterized by relatively weak fluoride binding (e.g.K = 35.8 +/- 9.8 M(-1) for FcBO2C2H2Ph2-S,S), and by cathodic shifts in the ferrocene oxidation potential that form the basis for electrochemical or colorimetric fluoride detection. The fluoride selectivity of these systems is attributed to relatively weak Lewis acidity, resulting in weak F- binding, and essentially no binding of potentially competitive anions. By contrast, more elaborate Lewis acid frameworks based on calix[4]arene (calixH4), such as (FcB)2calix or fcB2calix, do not survive intact exposure to standard fluoride sources (e.g. [nBu4N]F.xH2O solutions in chloroform or acetonitrile). Instead B-O bond cleavage occurs yielding the parent calixarene; the differences between alkoxo- and aryloxo-functionalised derivatives can be rationalised, at least in part, by consideration of the differences in electron donating capabilities of RO- (R = alkyl, aryl).

Synthetic approaches based on the direct borylation of ferrocene by BBr(3), followed by boryl substituent modification, or on the lithiation of ferrocene derivatives and subsequent quenching with the electrophile FBMes(2), have given access to a range of ferrocene derivatized Lewis acids with which to conduct a systematic study of fluoride and cyanide binding. In particular, the effects of borane electrophilicity, net charge, and ancillary ligand electronics/cooperativity on the binding affinities for these anions have been probed by a combination of NMR, IR, mass spectrometric, electrochemical, crystallographic, and UV-vis titration measurements. In this respect, modifications made at the para position of the boron-bound aromatic substituents exert a relatively minor influence on the binding constants for both fluoride and cyanide, as do the electronic properties of peripheral substituents at the 1'- position (even for cationic groups). By contrast, the influence of a CH(2)NMe(3)(+) substituent in the 2- position is found to be much more pronounced (by >3 orders of magnitude), reflecting, at least in part, the possibility in solution for an additional binding component utilizing the hydrogen bond donor capabilities of the methylene CH(2) group. While none of the systems examined in the current study display any great differentiation between the binding of F(-) and CN(-) (and indeed some, such as FcBMes(2), bind both anions with equal affinity within experimental error), much weaker boronic ester Lewis acids will bind fluoride (but give a negative response for cyanide). Thus, by the incorporation of an irreversible redox-matched organic dye, a two-component [BMes(2)/B(OR)(2)] dosimeter system can be developed capable of colorimetrically signaling the presence of fluoride and cyanide in organic solution by Boolean AND/NOT logic.

The activation of N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diamino Co(II), [Co(II)(1)], by the addition of acetic acid under aerobic conditions has been investigated by a range of spectroscopic techniques including continuous-wave EPR, HYSCORE, pulsed ENDOR, and resonance Raman. These measurements have revealed for the first time the formation of a coordinated cobalt(III)-bound phenoxyl radical labeled [Co(III)(1(*))(OAc)(n)](OAc)(m) (n = m = 1 or n = 2, m = 0). This cobalt(III)-bound phenoxyl radical is characterized by the following spin Hamiltonian parameters: g(x) = 2.0060, g(y) = 2.0031, g(z) = 1.9943, A(x) = 17 MHz, A(y) = 55 MHz, and A(z) = 14 MHz. Although the radical contains coordinated acetate(s), the experiments unambiguously proved that the phenoxyl radical is situated on ligand (1) as opposed to a phenoxyl radical ligated to cobalt in the axial position. Density functional theory computations on different models corroborate the stability of such a phenoxyl radical species and suggest the ligation of one or two acetate molecules to the complex. A mechanism is proposed, which accounts for the formation of this unusual and extremely robust phenoxyl radical, never previously observed for [Co(1)].